Name _________________________________________________ Class _____________________ Date _____________________________
Energy Flow Relationships
If an ecosystem is to be self – sustaining it must contain a constant supply of energy
which is available to all the organisms within the ecosystem. The energy must flow from
organism to organism.
Green plants convert radiant
energy from the Sun into chemical energy
(food). A food chain involves the transfer
of energy from green plants through a
series of organisms with repeated stages
of eating and being eaten. The energy
moves in one direction through the food
chain. For example, green grass obtains
its energy directly from sunlight; in turn,
a grasshopper obtains its energy from the
grass (plant); a snake uses the grasshopper as its energy source; and
finally when the snakes dies, its remains may be consumed by bacteria and
fungi providing them with an energy source and recycling materials back
into the ecosystem.
In an actual natural community, the flow of energy and materials is
more complicated than the food chain example. Since organisms may be
consumed by more than one species, many interactions occur among the
food chains in any community. These interactions are described as a food
web (see diagram). Interactions involve:
Producers (autotrophs): use the suns energy to convert CO2 into C6H12O6.
Consumers: Primary consumers or herbivores get their energy by eating
green plants. Secondary consumers or carnivores, feed upon other consumers. Omnivores eat
both plants and other animals.
Decomposers: Includes bacteria
and fungi, which are
responsible for breaking down
dead organisms and
releasing the nutrients into the
soil. They can break
down any organism.
A pyramid of energy can
be used to illustrate the
loss of energy at each feeding
level. For example, there
must be much more energy at
the producer level in a
food web than at the consumer
levels. Each consumer
level of the food pyramid
utilizes approximately 10
% of its ingested (eaten) nutrients to build new tissue. This new tissue represents the food for
the next feeding level. This means that each level only passes on about ten percent of the
energy it received. The remaining energy is lost in the form of heat and unavailable chemical
energy.
Eventually, the energy from an ecosystem is lost and is radiated from the Earth’s system.
Thus, an ecosystem cannot sustain itself without the constant input of energy from the Sun.
Name _________________________________________________ Class _____________________ Date _____________________________
Complete the following questions.
1. Which diagram A or B most accurately represents interactions between biotic and abiotic
factors in a forest environment? Support your answer.
Diagram: _________
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2. State what would most likely happen to one other population in this food web if all the
squirrels and rabbits were suddenly killed by a viral disease. Support your answer.
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3. If this forest community experienced severe lack of rain throughout the spring and summer,
state what affect this drought could have on the grouse population. Support your answer.
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4. State one possible reason why the deer population could remain relatively constant even
though the number of berry bushes and berries varies from year to year.
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